Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $5.35   11.200%   $5.9492   $5.95   $5.95   $5.90  
  Purchase #2 $229.64   13.466%   $260.5633   $260.56   $260.55   $260.60  
  Purchase #3 $212.83   4.735%   $222.9075   $222.91   $222.90   $222.90  
  Purchase #4 $150.26   3.857%   $156.0555   $156.06   $156.05   $156.10  
  Purchase #5 $12.64   9.556%   $13.8479   $13.85   $13.85   $13.80  
  Purchase #6 $47.64   5.858%   $50.4308   $50.43   $50.45   $50.40  
  Purchase #7 $166.81   5.837%   $176.5467   $176.55   $176.55   $176.50  
  7 purchase totals = $825.17       $886.3009   $886.31   $886.30   $886.20